Sound reproduction techniques of mobile multimedia have been improved with the development of mobile communication technologies, as a result of which high performance, high sound quality and high power are required of a micro speaker.
In most cases, a conventional micro speaker does not use a special suspension to ensure a lightweight of a diaphragm and connects a lead wire of a voice coil to the diaphragm via bonding to apply external electric signals to the voice coil. Therefore, unbalanced vibration is often generated due to the absence of the suspension, and the lead wire of the coil is often down in high power due to a tensile force, which makes it difficult for the micro speaker to be applied to high power.
In order to solve the foregoing problem, there has been developed a micro speaker using a suspension provided with a conductive pattern for transmitting electric signals. In the case of the micro speaker using the suspension, an increase in weight of the diaphragm, which results from the use of the suspension, leads to a decrease in sound pressure of the micro speaker. In addition, cracks may occur in the conductive pattern in high power, causing a defect.
FIG. 1 is a view showing a shape of a voice coil and a lead wire used in a conventional suspension type micro speaker, FIG. 2 is a view showing fabrication of a rectangular coil of FIG. 1, and FIG. 3 is a view showing a shape of a suspension used in the conventional micro speaker. As illustrated in FIG. 2, a circular voice coil 10 is changed to a rectangular voice coil 20 using a jig 30. Here, lead wires 22 and 24 of the voice coil 20 are positioned on the short side of the rectangular shape. Referring to FIG. 3, a suspension 40 includes an outer peripheral portion 42, an inner peripheral portion 46, and a connection portion 44 connecting the outer peripheral portion 42 to the inner peripheral portion 46. A conductive pattern 50 as well as land portions 60 for use in soldering or bonding the lead wires 22 and 24 of the voice coil 20 are formed on the surface of the suspension 40. In the conventional suspension 40, the land portions 60 for use in soldering or bonding the lead wires 22 and 24 of the voice coil 20 are formed on the connection portion 44 disposed on the short side adjacent to the positions of the lead wires 22 and 24 of the coil.
FIG. 4 is a view showing stress distribution of each portion that is generated in the event of vibration of the conventional suspension.
Here, it can be seen that a significant surface tension occurs inside the short connection portion 44 disposed on the short side of the suspension 40, as a result of which cracks may easily occur in the conductive pattern 50 formed on the surface of the suspension 40.